<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
   <p>整数1：<input id="num1" type="text"></p> 
   <p>整数2：<input id="num2" type="text"></p> 
   <p>
       <input type="button" value="相加" onclick="calc(add)">
       <input type="button" value="相减" onclick="calc(sub)">
       <input type="button" value="相乘" onclick="calc(mul)">
       <input type="button" value="相除" onclick="calc(div)">
   </p>
   <p>结果：<input id="result" type="text" readonly> </p>

   <script>
   function calc(func){
       var result=document.getElementById('result');
       var num1=parseInt(document.getElementById('num1').value);
       var num2=parseInt(document.getElementById('num2').value);
       if (isNaN(num1)||isNaN(num2)){
           alert('请输入数字');
           return false;
       }
       result.value= func(num1,num2);
   }
   function add(num1,num2){
       return num1+num2;
   }
   function sub(num1,num2){
       return num1-num2;
   }
   function mul(num1,num2){
       return num1*num2;
   }
   function div(num1,num2){
       if(num2===0){
           alert('除数不能为0');
           return ' ';
       }
       return num1 / num2;
   }
   </script>
</body>
</html>